As a hydraulic control apparatus having a switch valve for controlling supply and drainage of fluid to and from a single-acting cylinder, a hydraulic control apparatus used in, for example, a forklift is known. The hydraulic control apparatus may be employed for actuating a lift cylinder of the forklift, which selectively raises and lowers a fork, as described in Japanese Laid-Open Patent Publication No. 2002-327706.
The hydraulic control apparatus of the publication includes an operation check valve and a flow regulator provided in a main passage. The main passage connects a lift control valve, which is operated by means of a lift lever, to the lift cylinder. The lift control valve has a spool that includes a variable restrictor and is switched among a raising position, a neutral position, and a lowering position. More specifically, when the spool is located at the neutral position or the raising position, the lift control valve seals a back pressure chamber of the operation check valve. The operation check valve is thus urged in a direction for blocking the main passage. Meanwhile, a pump operates to apply hydraulic pressure to a second pressure chamber of the flow regulator and a valve body of the flow regulator is maintained at a fully open position.
In contrast, when the spool is located at the lowering position, a tank operates to apply hydraulic pressure to the back pressure chamber of the operation check valve. The operation check valve thus opens the main passage using the hydraulic pressure generated by the lift cylinder. Meanwhile, the hydraulic pressure in the tank is supplied to the second pressure chamber of the flow regulator. This causes the valve body of the flow regulator to move in such a manner that the difference between the pressure in a portion upstream from the variable restrictor and the pressure in a downstream portion is maintained equal to or lower than a predetermined value. The flow rate of the hydraulic oil flowing from the lift cylinder is thus adjusted.
However, in the hydraulic control apparatus, the operation check valve and the flow regulator are formed separately. Besides, the hydraulic control apparatus includes a large number of components and thus has a relatively complicated configuration. Further, since the operation check valve and the flow regulator must be accommodated separately in two different spaces, the hydraulic control apparatus becomes relatively large.